1. Field of the Invention
The present invention relates a photoelectric encoder.
2. Description of Related Art
A photoelectric absolute encoder that obtains an absolute position by detecting a pseudo-random pattern placed on a scale is known. As the pseudo-random pattern on the scale, a pattern called M-sequence code can be used for example (“Absolute position measurement using optical detection of coded patterns”, J T M Stevenson et. al, J. Phys, E:Sci. Instrum. 21(1988) 1140-1145). The absolute encoder disclosed in Japanese Unexamined Patent Application Publication No. H07-286861 guides an image of a pseudo-random pattern on a scale to a detector using a lens and thereby detects the position of the detector with respect to the scale. Further, the absolute encoder disclosed in Japanese Unexamined Patent Application Publication No. 2004-317503 uses a lens array instead of a lens.
Further, an absolute encoder having a structure with no lens is also known. The absolute encoder disclosed in Japanese Unexamined Patent Application Publication No. H05-71984 directly detects a light ray having passed through a pseudo-random pattern on a scale using a detection element.